Microsoft today began taking registration requests from Android tablet users for a beta of Office for Google's mobile operating system.

The final version, which Microsoft dubs "general availability," will be available in early 2015, Microsoft said, without naming a specific date or month. Meanwhile, the preview will be offered to those invited to the beta program within the next 7 days.

On the form potential preview participants were asked to fill out, Microsoft said that users must have an Android tablet with a screen size between 7-in. and 10.1-in. be running Android 4.4, aka KitKat; and forgo any OS updates during the time they use the preview.

Tablets running the just-released new Android 5, or Lollipop, are not eligible for the preview.

"There's really no reason why the apps shouldn't work on Lollipop," said J.R. Raphael, Computerworld's in-house Android expert who writes the Android Power blog. "But they may have created the apps with KitKat and don't want to take the risk of someone having problems on another edition."

On the form, Microsoft asked prospective participants the maker of their tablet and its screen size, questions intended to acquire a diverse group of testers.

Jan Dawson, principal analyst with Jackdaw Research, pointed out the different way Microsoft approached Office for Android from its launch of Office for iPad in March.

"When Microsoft released Office for iPad, it was just there. Office for Android has to go through several months of testing. That highlights the difficulty of developing something this complex for Android," said Dawson, pointing out the variety of screen sizes, operating system editions, screen resolutions and aspect ratios in the Android tablet market. "With the iPad, there were just two sizes," Dawson added as a comparison. "Developing for Android is a different challenge."

According to online reports -- a few media outlets and Microsoft-centric blogs were pre-briefed by the Redmond, Wash. company before today's announcement, a common move by the firm -- Office for Android will feature the same three core apps seen in the just-updated Office for iPad: Excel, PowerPoint and Word, with similar if not identical functionality.

Users will be able to view, create and edit documents in those three apps free of charge -- again, identical to the modified policies put in place for Office for iPad today -- but some business-oriented features will still require an underlying Office 365 subscription. And only Office 365 subscribers will be able to access the now-unlimited OneDrive storage space.

The KitKat requirement for the Office for Android preview will limit the beta to just under a third of all Android owners, as Google's latest statistics show that Android 4.4 powers 30.2% of all devices, smartphones and tablets combined.

Office for Android's preview will be made available for download via Google Play, Google's official app marketplace.

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